Enhanced cooling for downhole motors

ABSTRACT

A submersible pumping system for use downhole, wherein the system includes a pump, an inlet section for receiving fluid, a pump motor, and heat transfer fins on the motor housing. The fins increase the heat transfer area of the motor thereby providing enhanced cooling of the motor.

BACKGROUND

1. Field of Invention

The present disclosure relates to downhole pumping systems submersiblein well bore fluids. More specifically, the present disclosure concernsan improved method of cooling pump motors used to drive the submersiblepumping systems. Yet more specifically, the present disclosure involvesenhancing the surface area of the pump motor for increasing the heattransfer between the pump motor and the well bore fluid flowing acrossthe surface of the pump motor.

2. Description of Prior Art

Submersible pumping systems are often used in hydrocarbon producingwells for pumping fluids from within the well bore to the surface. Thesefluids are generally liquids and include produced liquid hydrocarbon aswell as water. One type of system used in this application employs anelectrical submersible pump (ESP). ESP's are typically disposed at theend of a length of production tubing and have an electrically poweredmotor. Often, electrical power may be supplied to the pump motor via anelectrical cable. Typically, the pumping unit is disposed within thewell bore above where perforations are made into a hydrocarbon producingzone. This placement thereby allows the produced fluids to flow past theouter surface of the pumping motor and provide a cooling effect.

With reference now to FIG. 1, an example of a submersible ESP disposedin a well bore is provided in a partial cross sectional view. In thisembodiment, a downhole pumping system 12 is shown within a cased wellbore 10 suspended within the well bore 10 on production tubing 34. Thedownhole pumping system 12 comprises a pump section 14, a seal section18, and a motor 24. The seal section 18 forms an upper portion of themotor 24 and is used for equalizing lubricant pressure in the motor 24with the wellbore hydrostatic pressure. Energizing the motor 24 thendrives a shaft (not shown) coupled between the motor 24 and the pumpsection 14. Impellers are coaxially disposed on the shaft and rotatewith the shaft within respective diffusers formed into the pump body 16.As is known, the centrifugal action of the impellers produces alocalized reduction in pressure in the diffuser thereby inducing fluidflow into the diffuser. In this embodiment, a series of inlets 30 areprovided on the pump housing wherein formation fluid can be drawn intothe inlets and into the pump section 14. The source of the formationfluid, which is shown by the arrows, are perforations 26 formed throughthe casing 10 of the well bore and into a surrounding hydrocarbonproducing formation 28. Thus the fluid flows from the formation 28, pastthe motor 24 on its way to the inlets 30. The flowing fluid contacts thehousing of the motor 24 and draws heat from the motor 24.

In spite of the heat transfer between the fluid and the motor 24, over aperiod of time the motor 24 may become overheated. This is especially aproblem when the fluid has a high viscosity, a low specific heat, and alow thermal conductivity. This is typical of highly viscous crude oils.The motor 24 may be forced to operate at an elevated temperature, pastits normal operating temperature, in order to reject the internallygenerated heat. This temperature upset condition can reduce motor lifeand results in a reduction in operational times of the pumping system.

SUMMARY OF INVENTION

The present disclosure includes a downhole submersible pumping systemcomprising, a pump, a pump motor coupled to the pump, and a heattransfer member disposed on the pump motor outer surface. The pumpingsystem is configured for being disposed within a well bore. The pumpingsystem may further comprise a fluid intake, wherein the fluid intake isconfigured to receive downhole fluid and is disposed adjacent the pumpmotor. The downhole fluid received by the intake may create a flowpathflowing across the heat transfer member that absorbs thermal energy fromthe heat transfer member. In one embodiment, the entire outer surface ofthe heat transfer member is fully contactable by wellbore fluid. Theheat transfer member may have a substantially rectangular cross section,a “T” shaped cross section, or it may be elongated and disposedsubstantially parallel to the pumping system axis. Optionally, the heattransfer member may be disposed at an angle to the pumping system axis.The system may further comprise a multiplicity of elongated heattransfer members disposed substantially parallel to the pumping systemaxis.

The present disclosure may include another embodiment of a wellborepumping system submersible in a downhole fluid, where the systemcomprises a housing, a pumping device disposed in the housing, an intakein fluid communication with the housing, wherein the intake providesfluid communication with the outside of the housing and the pumpingdevice inlet, a motor disposed in the housing mechanically coupling tothe pumping device and a heat conducting fin disposed on the housingadjacent to the motor, wherein the fin freely extends away from thehousing wherein its entire outer surface is in contact with the downholefluid. The wellbore pumping system may have a pump discharge thatcommunicates with production tubing.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a prior art downhole submersible system in a partial crosssectional view.

FIG. 2 shows a side view of a pumping system in accordance with thepresent disclosure disposed within a cased well bore.

FIG. 3 provides a schematic cross sectional view of a portion of thepumping system having a heat transfer member extending therefrom.

FIG. 4 shows a side view of a portion of the pumping system of thepresent disclosure illustrating fluid flow over a heat transfer member.

FIG. 5 is a cross sectional view of an embodiment of a heat transfermember.

FIG. 6 is a cross sectional view of an alternative embodiment of a heattransfer member.

FIG. 7 is an overhead view of an alternative view of a heat transfermember.

FIG. 8 is a side view of an embodiment of a pumping system havinglaterally disposed fins.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theillustrated embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be through and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

The present disclosure provides embodiments of a downhole submersiblepumping system for producing fluids from within a well bore up to thesurface. One embodiment of the pumping system disclosed herein includesa pump, an intake system for providing fluid intake to the pump, and amotor for providing a mode of force for the pump. The cooling systemdescribed herein is a largely passive system that can maximize the heattransfer surface area on the outer body of the submersible motor.Examples of a passive system include a heat transfer member, such as afin, extending along a portion of the length of the housing of themotor.

In FIG. 2, one embodiment of a pumping system with enhanced cooling isprovided in a side view. In this embodiment, the pumping system 40comprises a pump section 42, an inlet section 44, and a motor section48. The pump section includes a pump 43 shown in a dashed outline.Formed in the inlet section 44 are inlets 46 for providing a fluid inletpath to the pump 43. Examples of pumps useful in this system includecentrifugal pumps, positive displacement pumps, progressing cavity pumpsas well as multi-stage centrifugal pumps. With regard to the inletsection 44, the specific inlets 46 may comprise the circular orifices asshown, other embodiments may be included, such as elongated slits andother shaped orifices allowing fluid flow into the pumping unit. In thisembodiment production tubing 56 is included, thereby enabling fluidcommunication between the pumping system 40 and the surface.

With regard to the motor section 48 of FIG. 2, it comprises a motorhousing 50 that surrounds and protects a motor disposed therein.Provided on the outer surface in the housing 50 are a series of heattransfer members 52 for increasing the effective heat transfer surfacearea of the motor housing 50. Maximizing this heat transfer surface areathereby maximizes the heat transfer from the motor through the housing50 into the fluid flowing past these heat transfer members 52. In thisembodiment, the fluid is shown flowing into the well bore viaperforations 54 formed through the wellbore casing 39. Formation fluidfrom the formation 55 flows through the perforations 54 into thewellbore 38. The heat transfer members 52 of FIG. 2 are shown aselongated fins, however as will be discussed below, the members 52 cantake on many forms and are not limited in scope to the embodimentillustrated.

Heat transfer from the motor housing 50 to the flowing fluid can bemodeled with the following equation: Q=hcA(T_(s)−T_(f)). Here, Q equalsthe rate of heat transfer; hc equals the heat transfer coefficient; Aequals the surface area; T_(s) equals the temperature of surface; andT_(f) equals the temperature of the fluid. For a given amount of heatgenerated by the motor, increasing the surface area and/or the heattransfer coefficient can lower the operating temperature of the motorwithin the housing. The heat transfer coefficient represents the complexinteraction of the fluid thermophysical properties, the temperaturedifferentials, the velocity of flow and, and the geometry of the flowpath. The thermophysical properties of a fluid at any given temperatureare relatively fixed and unalterable. Increasing the velocity of flowhas only a small effect on the heat transfer coefficient of highlyviscous fluids.

In one embodiment of the heat transfer member disclosed herein, themember 52 outer surface is fully contacted by the fluid flowing past themember 52. Thus in this embodiment a single flow of fluid is in contactwith the member and receives thermal energy from the member 52, and thusthe pump motor 48. This configuration is also referred to herein as aheat transfer member that freely extends from the housing into thecooling fluid. The motor housing is normally formed of a steel materialthat is machined from a cylinder. The members 52 (or fins) may also beof steel or another material. Preferably the fins are a contiguous partof the motor housing 50. Alternatively the fins could be machined intothe housing if the housing initial configuration has extra thick walls.The number of fins, their length, protrusion, configuration etc., aredetermined by a combination of fluid mechanics considerations, the spaceavailable and heat transfer analysis. It is within the capabilities ofthose skilled in the art to determine fin number and configuration. Ingeneral the annular space between the motor housing and the casing innerdiameter determines the protrusion. In one embodiment, the fin lengthwill be substantially equal to the motor housing length.

FIG. 3 schematically illustrates an embodiment of a section of thepumping system having a single freely extending heat transfer member 52a rather than the plurality of fins shown in FIG. 2. This portion shownin FIG. 3 is a cross sectional axial view of a semi-circular section ofthe motor section 48 a with the heat transfer member 52 a also shown incross section. The heat transfer member 52 a extends along a radialplane of the axis of the motor housing 50 a. In this embodiment, theheat transfer member 52 a has a substantially rectangular cross section.Fluid flowing along the axis of the pumping system 40 a is illustratedby a series of dots 58. Arrows are shown illustrating the flow ofthermal energy from within the motor, through the heat transfer member52 a, and out into the fluid 58. This provides one illustration of howthe surface area of an added heat transfer member can increase heattransfer away from a motor 49.

FIG. 4, which illustrates an embodiment of the pumping section of FIG. 3from a side view, also illustrates heat transfer from the motor section48 into a surrounding fluid. In this embodiment, arrow A₁ illustratesfluid flow over a heat transfer member 52 a. A series of arrows,represented by A_(Q) illustrate thermal energy flowing from the motorsection 48 into the heat transfer member 52. The continuous flow ofthermal energy is further illustrated by arrows A_(Q1) being directedfrom the heat transfer member 52 into the flow of fluid. Preferably theheat transfer member 52 a extends substantially along the full length ofthe motor 48.

FIGS. 5 through 5 c illustrate some other alternative embodiments ofheat transfer members. FIG. 5 is a cross sectional view looking axiallyalong the length of a heat transfer member 52 b and the motor housing 50b. In this embodiment, the heat transfer member 52 b has a largelyrectangular base with a tapered top terminating into an outer edge 60.Such a taper may be useful in reducing dynamic frictional drag lossesalong the length of the motor section.

FIG. 6 illustrates an alternative embodiment, where the heat transfermember 52 c has a largely T-shaped cross section for further maximizingmotor housing surface area and thereby heat transfer. The heat transfermember 52 c comprises a web 62 extending from the motor housing 50 cthat supports a flange 64 perpendicularly disposed on its terminal end.

FIG. 7 shows an overhead view of one section of a heat transfer member52 d. In this embodiment, the leading edge 66 (lower portion) andtrailing edge 68 (upper portion) of the heat transfer member 52 d istapered, as well as its outer terminal edge 60 a, in an attempt toreduce dynamic pressure losses across the heat transfer member. The heattransfer member 52 d is shown disposed on an embodiment of the motorhousing 50.

It should be pointed out however that the arrangement of the heattransfer member can include any number of heat conducting elementsextending out from the body of the pumping system 40. These members arenot limited to being located on the motor section but can be includedalong any portion, or just a single portion of the pumping system 40.Moreover, the arrangement is not limited to a series of elongated finson the outer surface of the motor housing 50, but can be a series ofrelatively shortened members having a matrix like pattern along thelength of the housing. The arrangement of the heat transfer members(fins) is not limited to being substantially aligned with the pumpingsystem axis, but can take a helical arrangement around the body of themotor or can simply be at some lateral angle with respect to the lengthof the axis. Optionally, protrusions 53 may be included with anyembodiment of the fins herein for creating a turbulent boundary layeradjacent the fin surface for increasing heat transfer.

FIG. 8 illustrates an alternative embodiment of a heat transfer member52 e being disposed at an angle with respect to the axis of the motorsection 48 b. This angle can range from substantially coaxial and tosubstantially perpendicular to the axis of the motor section.

In one example of use of the present system of concept fins inaccordance with the embodiment of FIG. 2, were added to an electricalsubmersible pump motor. Temperature results of the finned motor weretested and compared with temperature results of an unfinned pumpingsystem. Mathematical heat transfer modeling and actual physical testingwas performed. The results of this analysis are outlined in thefollowing tables.

EXAMPLE 1

In one example, electrical submersible pumps with finned and unfinnedmotors were analyzed in a flowing fluid, wherein the fluid had thefollowing properties, a density of 62.0 lb/ft³, a viscosity of 0.00458lbm/ft sec, and a flow rate of 969.7 lbm/min. The flow velocity in thefinned annulus was 1.04 ft/sec and 0.928 ft/sec in the un-finnedannulus. Each motor outside diameter was 7.25 inch outside diameter witha 10.2 inch casing inner diameter. The analysis assumed 45 fins on thefinned motor, each fin being 82 inches long, 0.525 inches in height, and0.187 inches thick. The calculated temperature rise for the finned motorwas 27.67° F. and 91.78° F. for the unfinned motor.

EXAMPLE 2

In another example, two electrical submersible pumps having finned andan unfinned motors were analyzed in a flowing fluid having a temperatureof 40° F., density of 61.2 lb/ft³, a viscosity of 1.344 lbm/ft sec, aspecific heat of 0.48 btu/lbm ° F., thermal conductivity of 0.075 but/hrft ° F., with a flow rate of 2386.2 lbm/min. The fluid used in thisexample was oil. The flow velocity in the finned annulus was 2.89 ft/secand 2.46 ft/sec in the un-finned annulus. Each motor outside diameterwas 7.25 inch outside diameter with a 10.2 inch casing inner diameter.The motor horsepower was 1500 hp. The analysis assumed 57 fins on thefinned motor, each fin being 816 inches long, 0.5 inches in height, and0.2 inches thick. The calculated internal temperature for the finnedmotor was 193.56° F. with an external temperature of 94.82° F., thecalculated internal temperature was 577.77° F. for the unfinned motorwith an external temperature of 479.04° F.

EXAMPLE 3

In another example, two electrical submersible pumps having finned andunfinned motors were analyzed in a flowing fluid having a temperature of174° F., density of 61.2 lb/ft³, a viscosity of 0.15456 lbm/ft sec, aspecific heat of 0.48 btu/lbm ° F., thermal conductivity of 0.075 but/hrft ° F., with a flow rate of 2386.2 lbm/min. The fluid used in thisexample was oil. The flow velocity in the finned annulus was 2.89 ft/secand 2.46 ft/sec in the un-finned annulus. Each motor outside diameterwas 7.25 inch outside diameter with a 10.2 inch casing inner diameter.The motor horsepower was 1500 hp. The analysis assumed 57 fins on thefinned motor, each fin being 816 inches long, 0.5 inches in height, and0.2 inches thick. The calculated internal temperature for the finnedmotor was 327.56° F. with an external temperature of 228.82° F., thecalculated internal temperature was 711.77° F. for the unfinned motorwith an external temperature of 613.04° F.

EXAMPLE 4

Table 1 illustrates a comparison of simulated electrical submersiblepump temperature increases versus actual measured temperature increases.Two electrical submersible pumps were analyzed, one with a finned motorand one without.

TABLE 1 Calculated Measured Horse Velocity temperature rise temperaturerise Power (hp) Fin? (ft/sec) (° F.) (° F.) 50 Yes 2 3.4 4 50 No 2 6.3 975 Yes 2 5.1 5 75 No 2 9.5 12.5 100 Yes 2 6.8 5 100 No 2 12.6 15 130 Yes2 8.9 8 130 No 2 16.4 19

The results provided in Table 1 demonstrate good agreement between thecalculated and measured temperature rises. Additionally, these resultslisted in this table further illustrate the advantages of using a finnedmotor over an unfinned motor with an electrical submersible pump for thepurposes of lowering motor temperature.

FIG. 6 is a plot illustrating respective temperatures rises of finnedand unfinned motors versus the horsepower (HPf) the motor dissipates asheat. The analysis used to create the graphed values assumed a 7.25 inchmotor outside diameter, 45 fins being 0.525 inch high, 0.187 incheswide, and 82 inches long. The analysis further assumed a 2 rotor motorwith 100 hp, a flowrate of 117 gpm inside of a 10.2 inch inner diametercasing. The HPf values shown cover a range of motor loading from 46% to132% all at 84.8% motor efficiency.

It is to be understood that the invention is not limited to the exactdetails of construction, operation, exact materials, or embodimentsshown and described, as modifications and equivalents will be apparentto one skilled in the art. In the drawings and specification, there havebeen disclosed illustrative embodiments of the invention and, althoughspecific terms are employed, they are used in a generic and descriptivesense only and not for the purpose of limitation. Accordingly, theinvention is therefore to be limited only by the scope of the appendedclaims.

1. A downhole submersible pumping system comprising: a pump; a pumpmotor filled with a dielectric fluid; a seal section located between thepump and the motor for reducing a pressure differential between thedielectric fluid and pressure of wellbore fluid; and at least one heattransfer member disposed on the pump motor outer surface for immersionin the fluid of a wellbore. wherein the pumping system is configured forbeing disposed within a well bore.
 2. The pumping system of claim 1,wherein the heat transfer member protrudes outward from the motorrelative to a longitudinal axis of the motor.
 3. The pumping system ofclaim 2, wherein the heat transfer member extends substantially alongthe length of the motor.
 4. The pumping system of claim 2, wherein theheat transfer member extends along a portion of the length of the motor.5. The pumping system of claim 1, wherein the heat transfer member has asubstantially rectangular configuration in a transverse cross section.6. The pumping system of claim 1, wherein the heat transfer member has a“T” shaped transverse cross section.
 7. The pumping system of claim 1,wherein the heat transfer member is elongated and disposed substantiallyparallel to a longitudinal axis of the pumping system.
 8. The pumpingsystem of claim 1, wherein the heat transfer member is disposed at anangle to a longitudinal axis of the pumping system.
 9. The pumpingsystem of claim 1, wherein said at least one heat transfer membercomprises a plurality of fins disposed in radial planes substantiallyparallel to a longitudinal axis of the pumping system.
 10. The pumpingsystem of claim 1, wherein the heat transfer member has a tapered outeredge.
 11. A wellbore pumping system comprising: a string of tubing forextension into a well; an electrical submersible pump assembly suspendedon the tubing, the pump assembly having a rotary pump driven by anelectrical motor having a motor housing; and a plurality of finsdisposed on the motor housing and extending outward therefrom forimmersion in the wellbore fluid flowing to the pump.
 12. The pumpingsystem of claim 11, wherein the fins protrude outward from the motorrelative to a longitudinal axis of the motor.
 13. The pumping system ofclaim 11, wherein the fins extend substantially along the length of themotor.
 14. The pumping system of claim 11, wherein the fins have asubstantially rectangular configuration in a transverse cross section.15. The pumping system of claim 11, wherein the fins have a “T” shapedtransverse cross section.
 16. The pumping system of claim 11, whereinthe fins are elongated and disposed substantially parallel to alongitudinal axis of the pumping system.
 17. The pumping system of claim11, wherein the fins are disposed at an angle to a longitudinal axis ofthe pumping system.
 18. The pumping system of claim 11, wherein saidfins comprise are disposed in radial planes substantially parallel to alongitudinal axis of the pumping system.
 19. The pumping system of claim11, wherein fins have a tapered outer edge.
 20. A method of pumpingfluid from a well comprising: providing, a motor for an electricalsubmersible pump assembly with at least one heat transfer memberprotruding outward therefrom; coupling the motor to a pump to make upthe pump assembly, connecting the pump assembly to a conduit andlowering the pump assembly into a wellbore; and supplying power to themotor to rotate the pump, which draws well fluid past the motordischarges the well fluid into the conduit, the heat transfer memberbeing immersed in the well fluid as it flows past the motor to dissipateheat from the motor.
 21. The method of claim 20, wherein the heattransfer member protrudes outward from the motor relative to alongitudinal axis of the motor.
 22. The method of claim 20, wherein theheat transfer member extends substantially along the length of themotor.
 23. The method of claim 20, wherein the heat transfer member hasa substantially rectangular configuration in a transverse cross section.24. The method of claim 20, wherein the heat transfer member has a “T”shaped transverse cross section.
 25. The method of claim 20, wherein theheat transfer member is elongated and disposed substantially parallel toa longitudinal axis of the pumping system.
 26. The method of claim 20,wherein the heat transfer member is disposed at an angle to alongitudinal axis of the pumping system.